A contactless communication system has a reader and at least one contactless card. Communication protocols between the reader and the contactless card have been described in, for example, International Organization for Standardization (ISO) standards 14443, 15693, and/or 18000.
Each contactless card, also known as a chip card, smart card, RFID tag, or proximity IC card (PICC), typically has a single chip with a memory, which stores a unique user identification (UID) and data, and a radio transceiver or transponder with an antenna.
The reader, also called an interrogator, is a higher-power transceiver having a larger antenna to interrogate the contactless card with an interrogation or carrier signal. It is also possible for the reader to write to the contactless card and change the contactless card's data.
When the reader is turned on, the contactless card transmits its UID and possibly data by modulating a carrier signal received from the reader. Binary pulses representing the UID and data modify the impedance of the contactless card's antenna, which in turn causes an amplitude shift in the carrier signal. This process loads and unloads the contactless card antenna to reflect an impedance back into the reader antenna via the modulated carrier signal. This modulated carrier signal is then peak-detected at the reader and reshaped into a serial data signal.
Contactless communication systems feature anti-collision resolution, as multiple contactless cards transmitting simultaneously within the reader's antenna field can interfere with one another. Many available schemes prevent such collisions. One scheme uses a time-division multiplexed arrangement, assigning each contactless card a time slot in which to transmit. Also, collisions can be resolved by muting all contactless cards except the contactless card being read to ensure that no collision occurs. After a certain period of time, the muted contactless cards are reactivated.
It is difficult, if not impossible, to add physical memory to or change the contactless card's features in the field. The result is a manufacturer's choice between equipping the contactless card with a smaller memory and/or having fewer features, risking the contactless card may not meet future requirements, and equipping the contactless card with a larger memory and/or additional features, risking the initial version of the contactless card being more expensive than necessary.